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31.
This paper is dedicated to the comprehensive investigation on dented hemispheres under external hydrostatic pressure. A total of 20 stainless steel hemispheres are fabricated, which have a nominal radius of 60 mm and a nominal wall thickness of 0.76 mm. These fabricated hemispheres are divided into four groups with five samples in each group. Wherein, three groups are dented using conical, spherical, and cylindrical indenters respectively, while the remaining group is designated as undented one. Both dented and undented hemispheres are hydrostatically tested into collapse to examine the effects of indention on the collapse characteristics of hemispheres. Additionally, all tested hemispheres are semi-analytically and numerically evaluated based on the measured geometric data and tested material properties. The experimental, semi-analytical, and numerical results are compared in figures and tables. 相似文献
32.
Grounding experiments on soft bottoms 总被引:3,自引:0,他引:3
To verify a theoretical analysis procedure for calculation of the hull girder response of ships running aground, a series
of large-scale ship grounding experiments was performed on an artificial island made of engineered fill. The tests were conducted
by running a condemned fishing vessel up on selected beaches of the island with velocities ranging between 2m/s and 5.5m/s.
During the tests, surge, heave, and pitch accelerations were measured and also the deformations of the beach and the ship
bow. Based on these accelerations, rigid body velocities and motions were determined. The forces arising from the interaction
between the bow of the vessel and the seabed were determined by solving the equations of motions. This article describes the
analysis of the measured results and a comparison of the results from the full-scale measurements with results from a recently
developed analysis procedure for grounding on soft bottoms.
Presented at the International Conference on Technology for Marine Environment Preservation (MARIENV '95), Tokyo, Japan, September
24–29, 1995. 相似文献
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The stocks of principal groundfish species off New England have collapsed, creating economic hardship and dislocation in fishing communities from Rhode Island to Maine. In this article we analyze the causes of this collapse using the ?ratchet effect? described by Ludwig, Hilborn, and Walters (1993) as a framework. According to Ludwig, Hilborn, and Walters, powerful economic and political interests drive fisheries to overcapitalize and overexploit despite scientific evidence that stocks are declining. When the fishery is no longer economically viable, governments provide financial assistance to minimize economic hardship. When stocks increase there is another rush to invest, and the cycle repeats itself. The history of groundfish management in New England conforms well to this model. Optimism among fishers and government over U.S. control of this fishery in 1977 stimulated successive rounds of investment that built up excessive fishing capacity despite warnings from scientists that stocks were becoming weaker. Management regimes designed by the New England Fishery Management Council were ineffective in constraining fishing effort. Collapse of the stocks has led to severe restrictions on fishing and to government assistance. We suggest that the integration of science, management, and harvesting sectors through ecosystem-based management offers the best means of avoiding similar situations in the future. 相似文献
36.
百丈隧道左洞ZK152+433~ZK152+463段穿越流塑状富水破碎带施工时反复出现变形侵限、塌方等情况,给工程施工带来前所未有的挑战。文章详细阐述了施工过程中采取的各种处治措施,总结了不同处治方案和效果,并采用数值分析方法对隧道结构安全性进行了分析。结果表明:(1)对于流塑状富水破碎带,加密超前支护是防止开挖时围岩出现较大变形或者坍塌的最有效措施。百丈隧道流塑状富水破碎带最终采用了每榀钢架(钢架间距50 cm)都打设一环3.5 m长?51自进式锚杆的超前支护方式,即每个断面都有7层超前支护,最终有效控制了开挖后围岩变形,避免衬砌侵限与塌方;(2)对于流塑状富水破碎带,加固围岩尤其是边墙与基底处围岩非常重要,可有效减少开挖过程中衬砌的整体式下沉。采用抛石挤淤+注浆的方式进行边墙与基底围岩加固,其效果比采用单纯注浆方式好得多;(3)对于外部荷载较明确的隧道,采用计算分析结合工程经验的方式确定衬砌支护参数,既能保证隧道结构安全,又使其经济合理;(4)在双车道隧道施工中,采用三台阶法施工,应尽量缩短台阶长度,使初期支护及时封闭成环,从而可以较好地控制围岩变形。 相似文献
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针对湖南某电厂2 070 t/h对冲式燃烧超临界锅炉NOx排放过高的情况,对其进行了燃烧试验,分析了省煤器出口氧量体积分数、二次风开度、机组负荷、燃尽风开度等运行因素对锅炉燃烧及NOx排放特性的影响,在单因素较优方案下做了多因素变化对NOx排放影响的试验研究.试验结果表明:省煤器出口氧量体积分数、燃尽风开度和机组负荷对锅炉NOx排放质量浓度有十分显著的影响;随着省煤器出口、SAR入口之前的氧量体积分数的上升,NOx排放质量浓度表现为比较明显的上升规律;随着机组负荷的升高,NOx排放质量浓度表现为先升高后降低.通过设置不同的二次风配风方式、燃尽风开度等运行方式,得出该锅炉的NOx排放特性,从而降低NOx排放. 相似文献
39.
以XXX高速公路工程罗圈背隧道施工为背景,阐述了罗圈背隧道发生塌方的过程和状况,分析了塌方原因,并就塌方处理方案及技术进行了论述,以供类似工程参考。 相似文献
40.
Experimental assessment of the ultimate strength of a box girder subjected to severe corrosion 总被引:1,自引:0,他引:1
The objective of this paper is to describe the experimental assessment of the ultimate strength of a severely corroded box girder subjected to a uniform bending moment resulting from four-point loading. Three box girders that could simulate the behaviour of midship sections have been deteriorated in corrosive seawater environment to simulate different levels of corrosion degradation of ageing ship structures. During the deterioration process, various parameters have been controlled and the total weight lost was registered. Corroded plate thicknesses have been measured in 212 points and a statistical analysis has been performed. The resulting corrosion wastage has been fitted by a non-linear time variant degradation model. The experimental results of the ultimate strength test of a severely corroded box girder subjected to a four-point loading have been analysed. The load-displacement and moment-curvature relationship is discussed, different failure modes are identified, and the strain gauges readings are analysed. 相似文献